Greenland's butterflies are shrinking. What's causing it?

Add one more item to the list of strange global warming effects: Butterflies are shrinking. At least, that's what Danish researchers in Greenland have found while studying high-arctic butterflies. Between 1996 and 2013, they collected 4,500 butterflies annually in Northern Greenland and measured their wings. The pattern is clear: Wing length has decreased "significantly" in response to warmer summers.

"Our studies show that males and females follow the same pattern and it is similar in two different species, which suggests that climate plays an important role in determining the body size of butterflies in Northeast Greenland," says senior scientist Toke T. Høye, Aarhus Institute of Advanced Studies, Aarhus University.

AU/Rikke R. Hansen/Promo image

This phenomenon is probably not limited to butterflies, and some species are expected to become larger over time due to higher temperatures leading to longer feeding seasons. But we can't be sure of the effects on many species yet, as only very few field studies have been able to follow changes in the body size of the same species over a period where the climate has changed. As far as the scientists who conducted the study know,their work is the longest known time series on body size variation in butterflies.

So why are butterflies getting smaller rather than bigger?

"We humans use more energy when it is cold, because we must maintain a constant body temperature. But for butterfly larvae and other cold-blooded animals whose body temperature depends on the environment, the metabolism increases at higher temperatures because the biochemical processes are simply faster. Therefore, the larvae use more energy than they are able to gain from feeding. Our results indicate that this change is so significant that larval growth rate decreases. And when the larvae are smaller, the adult butterflies will also be smaller," explains Toke T. Høye.

The first photo at the top of this article shows the Arctic fritillary (Boloria chariclea), and the second one is of the Northern clouded yellow (Colias hecla). These are the two species studied by the researchers.